The present invention relates to a leader tape detecting circuit which positively detects the leader tape of a cassette tape which includes both leader tapes and a magnetic tape.
Cassette tapes commonly used in a tape recorder include a magnetic tape coated and magnetic particles and two leader tapes connected to the two ends of the magnetic tape. The leader tapes are made of a transparent material or a light reflecting material. In a cassette tape recorder, it is often desired to control recording and reproducing operations by detecting the leader tape. In this connection, a conventional leader tape detecting circuit employs a technique wherein the quantity of light which has passed through or is reflected by the tape leader is sensed to detect the presence of the tape leader when the quantity of light thus sensed is larger than a predetermined reference value.
In the conventional leader tape detecting circuit described above, the reference value is fixed. Therefore, the leader tape detecting circuit may operate erroneously depending on the particular tape cassette type or due to variations with time of the tape. More specifically, if a different tape is used, the amount of light which passes through or is reflected by the tape changes. The amount of this light tends to change greatly after the tape has been used for a long period of time or if the tape becomes dirty. As a result, the relation between the preset leader tape detecting reference value set in the tape recorder and the quantity of light detected becomes incorrect so that detection of the leader tape cannot be satisfactorily carried out.
Accordingly, an object of the invention is to provide a leader tape detecting circuit which can positively detect a leader tape of any kind of cassette tape under any conditions.